At the scene of a heinous crime, five suspects, one of whom is the guilty party, are being interrogated by a detective. Each of the suspects gives one statement and it later transpires that just three of these statements are correct.
These are the statements:
Uncle Jack: Uncle Jim committed the murder
Aunt Mary: I did not do it
Cousin Stewart: It was not Cousin Margaret
Uncle Jim: Uncle Jack is lying when he says I did it
Cousin Margaret: Aunt Mary is telling the truth
Who committed the murder?
Cousin Margaret. The statements of Aunty Mary, Uncle Jim and cousin Margaret are true.